Thermionic vacuum tube circuit for intercommunication systems



June 21, 1949. s. J. KLAPMAN THERMIONIC VACUUM TUBE CIRCUIT FOR INTERCOMMUNICATION SYSTEMS Flled Jan 11, 1947 INVENTOR. 501. J. ff/ZAPMAN 0m m ZOEkNrW Patented June 21, 1949 UNITED STATES PATENT OFFICE mnmmromomonum TUBE omourr FOR mT Rco moA'rIoN sYs'rEMs Sci J Klapman, Chicago, 111.

Application January 11, 19517, Serial No. 721,589

17 Claims.

This invention relates generally to amplifiers and has particular reference to the application of such amplifier tov inter-office communication systems.

In communication systems employing yacuum tubes as a means of amplifying voice currents it has been the practice to employ circuits which require that the filaments of the vacuum tubes used therein to be heated even during periods of no operation. Since the useful life of the tubes employed is proportional to the period when the filaments are heated, such systems are open to the objection that the useful portion of the life of the tubes usedtherein is only a small fraction of thepossible total life of the tubes.

In order to attain a large amount of useful tube life as compared to the total available tube life it has been the practice to have the'filaments heated only when the system is in use, that is, when actually used fohcommuhication between two or more stations. However, in such operation, it takes an inordinately long time for the filament to become heated and the system to become ready for operation and the ad,- vantages accruing from long life-,of the tubes in the system do not compensatefor the'delay or wait necessary for the systemtobe readyand operable.

With the foregoing considerations in mind it is an object of the present invention toprovide a communication system which will be practically instantaneously available for operation, and which will not require the consumptiomfof power by vacuum tubes used therein, except when they are being used in amplifying voice currents, to the end the tubes employed in ,the system will have a verylong useiuljlifeascompared to the total life of the tubes.

A further object is to provideanovelcircuit for a communication system whichwill create no power demand during periods ,when the system is not in actual use, but which willprovide for practically. immediate operation when the system is called into use.

A yetfurther object comprehends. a circuit for a communication system which will store va quantity of electrical energy which. will make the system immediately available forwoperation.

Still another object is to,pr.ov ide,in such. ,a communication system a circuitwhich operates as a filter against noises from an alternating current source and whichwill absorb.,a portion of the energy stored in the circuitwhenthasystem is called into operation.

2 ,Another object is to provide a circuit fora communication system, the circuit having means associated therewith for storing energy for in} stantly heating the tubes, the means thereafter being inactive and the tubes thereafter being heated in the normal manner.

Still another obj ect of the invention comprehends the provision of an amplifier for" each station of an intercommunication system, a single transducer being provided at each station for use alternately as a microphone and a loudspeaker, the transducer being connected to the inputof the station amplifier in talking; and to theoutput of a remote station in listening",

Other objects of the invention will be apparent from a studyoi the description hereinafter takentogether with thedrawings in which the single figureshows a schematic diagram of a five station"intercommunication system, two of the stations being shown in detail.

,Reierringnow to the drawing, there is shown Station A and Station B of a five station inintercornmunication system. Each station has as a part thereof a two stage amplifier consisting of a first stage of amplification, indicated generally by the ordinal l0, and a second stage of amplification, indicated generally by the ordinallZ. Power is supplied for the amplification stages l0 and I2 from an alternating current source I4, which is connected through an overload fuse [8 to a selenium rectifier l8 which provides a potential high enough to supply anode voltage.

The rectifier I8 is connected by a lead 20 to afilter network consisting of a resistor 22 and capacitors 24 and 26 where theiv oltage derived at the rectifier IB is suitably filtered.

Stations A and B, as are all the stations of the system, are each provided with a talklisten switch, indicated by the ordinal 28, which is ,of the three-pole, double-throw type, the switch ,28 being normally closed in the listen position as shown. In the other or talk position voltage is supplied by the rectifier 18 through an indicator lamp 30 and a dropping resistor 32, through conductors 34 and 36 tocathodes 38 and 40 of amplification stages [0 and I2, a dropping resistor 42 between the cathodes 38 and 40 bein provided to maintain the proper voltages thereacross.

The supply to the cathodes 38 and lllis suitablyfiltered by. means of capacitors 44, 46, and

48, capacitors 48, being of a large enough, capac ity for additional functions as will appearlater. ,'I'he arrangement thu far described provides suitable cathode, anode and grid voltages to a two stage amplifier, which under ordinary conditions would be available for operation within the usual warm-up period. However, as has been pointed out above, the normal time of warm-up is much too long for efficient use of an intercommunication system, and accordingly means are provided which will heat the tubes of amplifier stages l0 and [2 almost instantaneously, the tubes thereafter being ready for normal use. To this end, the rectifier I8 is connected to a capacitor 50, which when the switch 28 is in the listen position, will be charged at the voltage derived at the rectifier l8, this voltage being the same as the anode voltage derived for the amplification stage l0 and 12. When the switch 28 is moved to the talk position the charge stored in the capacitor 50 is released through the leads 34 and 36 to the cathode circuit comprising cathodes 38 and 40, the dropping resistor 42 and the filter network comprising capacitors 44, 4E, and 48. The initial surge of current arising from the discharge of the capacitor 50 is largely absorbed by the capacitor 48, which, is of a capacity larger than that required for ordinary filtering. Capacitor 48 must be of suflicient capacity to reduce the shock on the cathode 40 to well below the damage point, but must also be of low enough ca pacity that not too great a time interval is required in charging, which would result in too great a time lag before the system would be operative. The remaining surge of current arising from the discharge of the capacitor then serves to heat the cathodes 38 and 48 very quickly, thus making the amplification stages l0 and I2 in a condition for almost instantaneous operation. Thereafter, with the switch 28 in the talk position voltage is supplied to the cathode circuit through the indicator lamp 353, the dropping resistor 32 and the leads 34 and 35. It will be apparent that the operator is apprised of the ready condition of the system as soon as the indicator lamp 30 is illuminated.

In the system shown, each station is provided with a transducer 52, which operates as a n1icro-- phone with the switch 28 in the talk position, and as a loud speaker with the switch 28 in the listen position, which is conn cted through the talklisten switch 28 to a conductor 54 to the primary of an input transformer 56, the secondary of which is connected to a grid "'53 of tube 53. The output from tube It is capacity coupled to an input grid 552 of the second stage of amplification 12 through a volume control 54. The output from amplification stage 12 is connected by conductor 66 to the primary winding of an output transformer 68, the secondary of which is connected to conductor it! through the switch 28, and thence to a conductor '12 of a station selector indicated generally b the ordinal 14.

As shown, the station selector i4 is set for tall:- ing to Station B, and is connected by conductor 16 which connects to a conductor 38 of a cable connecting the five stations of the system and common to each of the stations of the system. Station B is in the listen position and the conductor 16 is connected to the talk-listen switch 28 of Station 13, and the amplified voice currents of Station A directl energize the transducer 52 of Station B. Station B is connected at its associated station selector for talk to Station A. When it is desired that Station B talk to Station A the operator has merely to move the talk-listen switch 28 of Station B to the talk position. It will be seen that regardless of the position of the selector switch 14 of Station A that communication will be had with that station alone. At such time as the talk-listen switch 28 of Station B is moved to the talk position the amplifier of Station B will be instantaneously available for amplifying voice currents developed in the transducer 52 of Station B and deliver the so amplified voice currents to the transducer of Station A.

It will be apparent from the foregoing description that there has been provided an intercommunication system which is extremely efficient from the standpoint of tube life, and which is always instantaneously operable. While the invention has been described in terms of a preferred embodiment thereof, its scope is not limited in terms of the embodiment shown, nor otherwise than by the claims here appended.

I claim:

1. An amplifier for an intercommunication system comprising a plurality of thermionic tubes; anode, cathode, and grid electrodes for each of said thermionic tubes; a power source; means connected to said power source for supplying voltage at said anode and grid electrodes; a filter system incircuit with said cathode electrodes; a capacitor charged at the anode supply voltage when said tubes are in a non-emitting condition; and switch means for connecting said capacitor in circuit with said cathode electrodes for rapidly heating said cathode electrodes upon the discharge of said capacitor.

2. An amplifier for an intercommunication system comprising a plurality of thermionic tubes; anode, cathode, and grid electrodes for each of said thermionic tubes; a power source; means connected to said power source for supplying voltage at said anode and grid electrodes; a circuit for said cathode electrodes including capacitors therein for filtering undesirable voltages from said circuit; a capacitor charged at the anode supply voltage when said tubes are in a non-emitting condition; and switch means for connecting said capacitor in circuit with said cathode electrodes for rapidly heating said cathode electrodes upon the discharge of said capacitor, the discharge of said capacitor being subsequent to the application of the voltage at said anode and said grid electrodes by the said first means.

3. An amplifier for an intercommunication system comprising a plurality of thermionic tubes; anode, cathode, and grid electrodes for each of said thermionic tubes; a power source; means connected to said power source for supplying voltage at said anode and grid electrodes; a circuit for said cathode electrodes including capacitors therein for filtering undesirable voltages from said circuit; a capacitor charged at the anode supply voltage when said tubes are in a non-emitting condition; and switch means for connecting said capacitor in circuit with said cathode electrodes for rapidly heating said cathode electrodes; said circuit for said cathode electrodes having at least one capacitor therein for taking a portion of the surge current caused by operation of said switch means.

4:. An amplifier for an intercommunication system comprising a plurality of thermionic tubes; anode, cathode, and grid electrodes for each of said thermionic tubes; a power source; means connected to said power source for supplying voltage at said anode and grid electrodes;

" a circuit for said cathode electrodes including capacitors therein for filtering undesirable voltages-from said circuit; a capacitor charged at the'anode supply voltage when said tubes are in a non-emitting condition; and switch means for connecting said lastnamed capacitor in circuit "with said cathode electrodes for rapidly heating said cathode electrodes; said circuit for said cathode electrodes having at least one capacitor therein for taking a portion of the surge current caused by operation of said switch means; said cathode circuit being thereafter supplied from said power source.

5. -'An amplifier for an intercommunication system comprising a plurality of thermionic tubes; anode, cathode and grid electrodes for each of said thermionic tubes; a power source; means for rectifying current from said power source; a circuit including said means for supplying anode and grid voltages; a circuit including said cathodes having capacitors therein for filtering undesired voltages therefrom; a capacitor-charged at the anode supply voltage when said tubes are in a non-emitting condition; and switch means for connecting said capacitor in circuit with said cathode electrodes for rapidly heating said cathode electrodes upon the discharge of said capacitor.

:6. An amplifier for an intercommunication system comprising a plurality of thermionic tubes;anode, cathode and grid electrodes for each of said thermionic tubes; a power source; means for 'rectifying current from said power source; ia circuit including said means for supplying anode and grid voltages; a circuit including said cathodes having capacitors therein for filtering undesiredvoltages therefrom; a capacitor charged at the anode supply voltage when said tubes are inanon-emitting condition; and switch means for connecting said capacitor in circuit with said cathode electrodes; said circuit for said cathode electrodes having at least one capacitor therein for taking-a portion of the surge current caused by operation of said switch means.

' 7. An amplifier for an intercommunication system comprising a plurality of thermionic tubes; anode, cathode and grid electrodes for each of said thermionic tubes; a power source; means for rectifying current from said power source; a circuit including said means for supplying anode and grid voltages; a circuit including said cathodes havingcapacitors therein for filtering undesired voltages therefrom; a capacitor charged at the anode supply voltage when said tubes are in a non-emitting condition; and switch means for connecting said last named capacitor in circuit with said cathode electrodes; said circuit for said cathode electrodes having at least one capacitor therein for taking a portion of the surge current" caused by operation of said switch means and the discharge of saidlast named capacitor; said cathode circuit being thereafter supplied from said rectifying means.

8. In an intercommunication system of the type having a plurality of stations; each station being provided with an amplifier and a transducer capable of being connected to the input of its associated amplifier; said transducer being also capable of being connected to the output of an amplifier of a remote station; said amplifier comprising at least one thermionic tube; anode, cathode and grid electrodes for said thermionic tube; a power source; means for rectifying current from said power source; a circuit including said means for supplying anode and grid voltages; a circuit including said cathode electrode having 'capacitors therein for'filtering undesired voltages therefrom; a capacitor charged atthe anode supply voltage-when said tubesare in a non-emitting condition; and switch means for connecting said last named capacitor in circuit-with said cathode-electrode for'rapidly heating said cathode electrode upon the discharge of said last named capacitor.

non-emitting condition; and switch means for connecting said lastnamed capacitor in circuit with said cathode electrodes; said circuit for said cathode electrodes having at least one capacitor therein for taking a portion of the surge current caused by operation of said switch means; said last named capacitor in'said cathode electrode circuit being of sufiicient capacity to eliminate the shock on one of cathodes and of a suificiently small capacity to maintain the period of charge thereon at aminimum consistent with maintaining the surge against said cathode belowthe damage point.

-10. In an intercommunication system of the type having a plurality of stations; each station being provided with an amplifier and atransducer'capable'of being connected to the input of its associated amplifier; said transducer being also capable of being connected to the output of an amplifier of a remote station; said amplifier comprising a plurality of thermionic tubes;

I anode, cathode and grid electrodes for each of said thermionic tubes; a power source; means for rectifying current from said power source; a circuit including said means for supplying anode and grid voltages; a circuit including said cathodes having capacitors therein for filtering undesired voltagestherefrom; a capacitor charged at the anode supply voltage when said tubes are in a non-emitting condition; and switch means for connecting said capacitor in circuit with said cathode electrodes for rapidly heating said cathode eiectrodes upon the discharge of said capacitor; said circuit for said cathode electrodes having at least one capacitor therein for taking a portion of the surge current caused by operation of said switch means.

.11. In an intercommunication system of the type having a plurality of stations; each station being provided with an amplifier and a transducer capable of being connected to the input of its associated amplifier; said transducer being also capable of being connected to the output of an amplifier of a remote station; said amplifier comprising at least one thermionic tube;

anode, cathode and grid electrodes for said thermionic tube; a power source; .means for rectify- :ing current from. said power-source; a circuit including said means for supplying anode and grid voltages; a circuit including said cathode electrode having capacitors therein for filtering undesired voltages therefrom; a capacitor charged at the anode supply voltage when said tubes are in a non-emitting condition; and switch means for connecting said capacitor in circuit with said cathode electrodes for rapidly heating said cathode electrodes upon the discharge of said capacitor; said circuit-for said cathode electrode having at least one capacitor therein for taking a substantial portion of the surge current caused by operation of said switch means, said cathode circuit being thereafter supplied from said rectifying means.

12. In an intercommunication system of the type having a plurality of stations; each station being provided with an amplifier and a transducer capable of being connected to the input of its associated amplifier; said transducer being also capable of being connected to the output of an amplifier of a remote station; said amplifier COn'lpllSlll a plurality of thermionic tubes having anode, cathode and grid electrodes; 9. power source, means for rectifying current from said power source; a circuit including said last named means for supplying anode and grid voltages; a circuit including said cathode electrodes having capacitors therein for filtering undesired voltages therefrom; a capacitor charged at the anode voltage when said tubes are in a non-emitting condition; switch means normally connecting the transducer of an adjacent station to the output of a remote station; said switch means being operable to connect the output of its associated station to the transducer of a remote station; said switch means being also operable to connect said last named capacitor in circuit with said cathode electrodes for rapidly heating said cathode electrodes upon the discharge of said last named capacitor.

13. In an intercommunication system of the type having a plurality of stations; each station being provided with an amplifier and a transducer capable of being connected to the input of its associated amplifier; said transducer being also capable of being connected to the output of an amplifier of a remote station; said amplifier comprising a plurality of thermionic tubes having anode, cathode and grid electrodes; a power source; means for rectifying current from said power source; a circuit including said last named means for supplying anode and grid voltages; a circuit including said cathodes having capacitors therein for filtering undesired voltages therefrom; a capacitor charged at the anode supply voltage when said tubes are in a non-emitting condition; switch means normally connecting the transducer of an adjacent station to the output of a remote station; said switch means being operable to connect the output of its associated station to the transducer of a remote station; said switch means being also operable to connect said last named capacitor in circuit with said cathode electrodes for rapidly heating said cathode electrodes upon the discharge of said last named capacitor; the cathode electrode circuit having at least one capacitor therein for taking a portion of the surge current caused by the operation of said switch means.

14. In an intercommunication system of the type having a plurality of stations; each station being provided with an amplifier and a transducer capable of being connected to the input of its associated amplifier; said transducer being also capable of being connected to the output of an amplifier of a remote station; said amplifier comprising a plurality of thermionic tubes having anode, cathode and grid electrodes; a power source, means for rectifying current from said power source; a circuit including said last named means for supplyin anode and grid voltages; a circuit including said cathode electrodes having capacitors therein for filtering undesired voltages therefrom; a capacitor charged at the anode supply voltage when said tubes are in a nonemitting condition; switch means normally connecting the transducer of an adjacent station to the output of a remote station; said switch means being operable to connect the output of its associated station to the transducer of a remote station; said switch means being also operable to connect said last named capacitor in circuit with said cathode electrodes for rapidly heating said cathode electrodes upon the discharge of said last named capacitor; the cathode electrode circuit having a capacitor therein of sufiicient capacity to reduce the shock on said cathode eletrodes and of sufilciently small capacity to maintain the period of charge thereon at a minimum consistent with maintaining the surge against said cathodes below the damage point.

15. In an intercommunication system of the type having a plurality of stations; each station being provided with an amplifier and a transducer capable of being connected to the input of its associated amplifier; said transducer being also capable of being connected to the output of an amplifier of a remote station; said amplifier comprising a plurality of thermionic tubes having anode, cathode and grid electrodes; a power source; means for rectifying current from said power source; a circuit including said last named means for supplying anode and grid voltages; a circuit including said cathodes having capacitors therein for filtering undesired voltages therefrom; a capacitor charged at the anode supply voltage when said tubes are in a non-emitting condition; switch means normally connecting said transducer to the output of a remote station; said switch means being operable to connect the output of its associated station to the transducer of a remote station, said switch means being also operable to connect said last named capacitor in circuit with said cathode electrodes for rapidly heating said cathode electrodes upon the discharge of said last named capacitor; said circuit having at least one capacitor of sufiicient capacity therein for taking a portion of the surge current caused by the operation of said switch means; said cathode circuit bein thereafter supplied from said rectifying means.

16. The invention as defined in claim 13 wherein means are provided for indicating the operability of said amplifier immediately after the operation of said switch means.

17. The invention as defined in claim 15 wherein means are provided for indicating the operability of said amplifier immediately after the operation of said switch means.

SOL J. KLAPMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,055,921 Baker Sept. 29, 1936 2,222,196 Vilkomerson Nov. 19, 1940 2,378,311 McCreary June 12, 1945 

